1. Field of the Invention
The present invention relates to a push-switch having a light click feel used in operation parts of various electronic appliances.
2. Background Art
Switches used in operation parts of various electronic appliances are mostly so-called push-switches having a dome-shaped movable contact made of an elastic thin metal plate capable of assuring a light click feel in operation, and a low contact resistance value.
For example, a conventional push-switch disclosed in Unexamined Japanese Patent Publication No. 2000-294079 is described below by referring to FIG. 8 to FIG. 10.
FIG. 8 is a sectional view of the conventional push-switch. In the diagram, switch case 1 is made of an insulating resin formed by inserting, by exposing middle fixed contact 2 and two outside fixed contacts 3 at both sides across middle fixed contact 2, in a concave inner bottom of an upper opening. Terminals 4 linking to middle fixed contact 2 and outside fixed contacts 3 are individually extended outward.
Circular dome-shaped movable contact 5 formed of an elastic thin metal plate bulging upward at its middle has its outer circumferential lower end placed on outside fixed contacts 3, and the downside of the dome-shaped peak part is opposite to middle fixed contact 2 across a spacing. Drive body 6 has circular columnar operation part 6B projecting at the upside middle of flat plate part 6A and small circular columnar pressing part 6C projecting at the downside middle, and pressing part 6C at the downside is abutting against the dome-shaped peak part of movable contact 5.
Operation part 6B of drive body 6 projects from middle hole 7A, and cover 7 of metal plate is fitted to cover the concave upside of switch case 1 from the upside of flat plate 6A, and the conventional push-switch is formed.
The operation of the conventional push-switch having such configuration is described below. The following explanation is based on FIG. 9, in which the axis of abscissas denotes the operation stroke, that is, the pressing distance, and the axis of ordinates represents the pressing force.
From an ordinary state (point O) free of pressing force, when a pressing force is applied from above to operation part 6B of drive body 6, the dome-shaped peak part of movable contact 5 is pressed by downside pressing part 6C. When this pressing force exceeds the elastic deformation force (point P) of movable contact 5, the dome-shaped portion projects downward and is inverted elastically along with a click feel, and the downside of the dome-shaped peak part contacts with opposite middle fixed contact 2. As a result, outside fixed contacts 3 and middle fixed contact 2 conduct with each other by way of movable contact 5, so that the switch is turned on.
Then, releasing the pressing force gradually, when the pressing force becomes smaller the self-restoring force (point Q) of movable contact 5, the dome-shaped portion of movable contact 5 projecting downward bulges upward along with a click feel to restore elastically into a dome shape, leaving from middle fixed contact 2, so that the switch is turned off.
The percentage of the relation of elastic deformation force (P) and self-restoring force (Q), (P−Q)/P, is the click rate, and when it is in a range of 35% to 65%, it is favored as a light and responsive click feel.
In the conventional push-switch, a favorable click feel is obtained by pressing the dome-shaped peak part of movable contact 5. Although a favorable click feel is obtained by pressing the upside region of operation part 6B corresponding to the region of forming pressing part 6C at the downside of drive body 6, as the pressing position is deviated from the region of pressing part 6C, the click feel becomes poor.
This phenomenon is explained in FIG. 10. FIG. 10 is a relation diagram in which the axis of abscissas denotes the eccentric amount of the pressing position from the center of the switch (the center of switch case 1), and the axis of ordinates represents the click rate, and point O of the eccentric amount is the pressure at the central position of the switch, and the minus side shows the moving amount of the pressing position to the leftward direction in FIG. 8.
The conventional push-switch measured in FIG. 10 was 1.2 mm in diameter of pressing part 6C of drive body 6, and 3 mm in diameter of operation part 6B. When the eccentric amount of deviating the pressing position to operation part 6B from the center of the switch was in a range of −0.6 mm to 0.4 mm, the click rate was maintained at 35% to 65%, but at the pressing position exceeding the specified range of the eccentric amount, the click rate was low, and the click feel was dull. In this result, the numerical value of the eccentric amount was different between the plus side and the minus side, which is estimated due to deviation of the combination state of switch case 1 with drive body 6 in a horizontal direction.
This dull state of click feel may be estimated as follows. When the pressing position of operation part 6B is at an outer side from the position of pressing part 6C for pressing movable contact 5, the upside end of flat plate 6A at the opposite side of the pressing position becomes the fulcrum, and drive body 6 is inclined, and the pressing position of movable contact 5 is deviated from the dome-shaped peak part. At the same time, as compared with the pressing amount (operation stroke) of drive body 6, the downward deflection amount (moving extent) of the dome-shaped portion of movable contact 5 becomes smaller, and the pressing position downside of movable contact 5 abuts against the inner bottom of switch case 1. Hence, it is estimated that favorable click feel is not obtained.
To solve this problem, it is an idea to change the dimensional relation of operation part 6B and pressing part 6C of drive body 6, but the dimension of the dome-shaped peak part must be increased by increasing the diameter of circular dome-shaped movable contact 5, and the size cannot be reduced. Or when operation part 6B is formed in a smaller diameter than pressing part 6C, an allowable region for pressing to operation part 6B is too narrow, and the deviation of the mounted electronic appliance cannot be absorbed.